What is causing this unexpected shading in 3D view?
There's a few things.

The normals of the faces in those sections are pointing in the opposite direction of the normals around it, but that's not the problem you describe, however it might be a problem later, best deal with it anyway. You can flip selected faces, if 'recalc normals' doesn't quite get all of them.

There seems to be a Vertex Color layer, with specifically those faces coloured. Press the minus on this. That will wipe the vertex colours. 



How this happened? Being new to an application it is probable that you accidentally went into vertex paint mode a few times.